In known damping devices in printing machines, the dampening of the printing form is performed by dosing the dampening solution by a swingable damping roller.
The transfer roller is alternatingly in contact with the bathing cylinder, from which the dampening solution is received, and the distributing roller, to which the dampening solution is transferred. The quantity of the transferred solution is controlled by changing the time of contact of the transfer roller with the bathing cylinder.
The disadvantage of the device is that the dosing is performed by strokes, this causing a fluctuation of the quantity of the solution fed to the printing form, whereby the quality of the printing is unfavorably affected. A further disadvantage of the device lies in the different circumferential speeds of the bating roller and the distributing roller, this being the reason why the transfer roller must alternate its circumferential speed, upon contact with said rollers. Thereby, a mutual slippage and chafing of the surface on the textile cover of the transfer roller is caused. This chafing of the surface reduces the capability of receiving and transferring the dampening solution. A further disadvantage of this device is that it is not suitable for dampening by alcohol.
There are other known dampening devices, in which the dampening solution is transferred to the printing plate in a contactless manner by brush rollers, resilient wires, or nozzles. The quantity of the transferred dampening solution is controlled by changing the springing of the hairs on the brush rollers, or possibly by changing the size of the slit, through which the solution is projected to the dampening rollers, by screening sheets.
The disadvantage of these known devices is that the hairs of the brush rollers are frequently broken, the wires released, or the nozzles clogged. All these failures negatively influence the uniformity of dampening, and thus, also the quality of printing.